This invention relates to dynamic seals for containing fluid under pressure between a housing and a shaft adapted to be rotated relative to the housing. More particularly, it relates to such seals for pumps which include an expeller or repeller that pumps the sealed fluid away from the seal cavity during pump operation. Dynamic seals are used to establish a leak-proof barrier between stationary housing and rotatable shaft components. One typical form of dynamic seal has annular sealing rings respectively sealed and keyed relative to the housing and to the shaft. The relative rotation takes place across annular sealing faces formed on the sealing rings, and the sealing faces are adapted to cooperate closely with and be biased against one another, to minimize fluid leakage between the faces. The mutually sliding sealing faces generate friction, possible over-heating problems and wear.
In certain pumps for liquids an expeller on the rear face of the pump impeller is used to pump liquid from the seal area. The expeller operates somewhat as an impeller, to evacuate the liquid away from the rotating shaft and create a back pressure sufficient to overcome the contained liquid pressure.
In operation, the relative pressures are such that the impeller draws substantially all fluid from the seal area and delivers it to the pump outlet. In such applications, no particular dynamic shaft seal is required during the operating mode since no fluid can leak along the shaft. When the pump shaft is stationary, however, as when shut down, a physical barrier to leakage along the shaft is required.
Expellers thus have great appeal in containing liquid having a high degree of internal abrasion, as no dynamic seal need be used when the shaft is rotating. However, as soon as the shaft rotation is stopped, making the expeller ineffective, some form of dynamic seal may be needed.